The present invention relates to a flow imaging method by means of an MRI apparatus (hereinbelow called simply flow imaging method and in particular to a flow imaging method and an apparatus for realizing same suitable for blood flow imaging in a human body, etc.
Heretofore, as a blood flow imaging method by means of an MRI apparatus, several methods are generally known, by which an object image is obtained by using a plurality of images having different properties such as represented by an example, by which only the blood flow part is extracted by subtracting one from the other of an image obtained by using a pulse sequence sensitive to a flow and an image obtained by using another pulse sequence, which is not sensitive to the flow.
As one of these method, there is known a method discussed in Magnetic Resonance In Medicine 4, pp. 193-202 (1987). By this method a blood flow image is obtained by using a pulse sequence of radio frequency pulses applied at 180.degree., 90.degree., 180.degree. and by subtracting one from the other of images obtained by 2 measurements in the case where the first 180.degree. pulse is used as a selective exciting pulse, by which only the region within the field of view is excited, and the case where it is used as a non-selective exciting pulse, by which a region outside of the field of view is also excited, whereby the component of blood flow excited by the non-selective exciting pulse and pouring in the region within the field of view is imaged.
Further the bolus tracking method is a method, by which, in the spin echo method, the selection plane by the 90.degree. pulse is selected so as to be perpendicular to the blood flow direction and the selection plane by the 180.degree. pulse is selected so as to be parallel to a blood vessel and to include the blood vessel, blood subjected to the 2 exciting pulses being imaged. Although by this method, differing from the subtraction method, it is possible to image blood flow by one measurement, the part, which is imaged, is only a part, where the selection plane by the 90.degree. pulse intersects the selection plane by the 180.degree. pulse, and a part of blood flow, which moves after having been excited by the 90.degree. pulse and is excited again by the 180.degree. pulse. By this method the part of blood blow, which is imaged, is smaller than that imaged by the subtraction method. Consequently this method is used more often in order to measure the flow speed, based on the distance of movement of blood flow and the time interval between the two pulse applications than in order to know the distribution of blood vessel.
Between the prior art techniques described above the subtraction method had a problem that a plurality of images having different properties are necessary and that measurement time for obtaining an object image is long. On the other hand, the bolus tracking method had a problem that although it is unnecessary to effect any subtraction, only blood flow in a restricted region can be observed and it is not possible to observe blood flow sufficient for obtaining blood flow projection.